The past of Berkner Island
The dinosaur chimera

The ongoing thaw of Antarctica's icy borders has recently brought many new paleontological discoveries, which are slowly filling the fossil gap of Antarctica.
An important milestone was reached with the partial deglaciation of the northern part of Berkner, the largest island of the continent: once believed to be just an ice rise caused by elevated seabeds, the glacial retreat has shown a much more complex condition. The northern border of Berkner was only partially submerged, with a dozen of small rocks (no larger than an average house) emerging from the sea surface. A geologic troupe was immediately sent to this sterile archipelago, to study its rock composition.
Berkner rocks were dated to the Maastrichtian, the last age of the Mesozoic Era, between 72-66 million years ago. Against all odds, these rocks have formed in a terrestrial environment, despite being found at sea level: the paleo-environment consisted of alluvial plains where a multitude of plant species, typical of the Antarctic flora community, was found. According to paleogeographic and paleoclimatic models, Berkner was a relatively large island even during the Mesozoic, with a cold oceanic climate comparable to modern-day Falkland. The territory was well separated from West and East Antarctica, which probably never had a direct connection with Berkner: this prolonged insular condition suggested the presence of a peculiar insular fauna. 

Paleontological research continued after 2200 in the geological formation of Berkner, which was named "High Rock Formation": however, the first exceptional finding was only made in 2899, with the discovery of an articulated hind limb, initially assigned to an unknown coelurosaur. Limb bones were robust and the unguals of the feet were curved, suggesting predatory behavior. In the subsequent year, a complete skull was discovered at the same fossil site, which allowed the erection of a new paleospecies... a bird species: Criolophornis magnicrus (Riminravenna, 2900). The resulting reconstruction of this bird, based on the skull and hind limbs, was incredibly bizarre: the species was described as an enantiornithe, an extinct group of birds known for their toothed beak, clawed wings, and primitive skull structure. The Crilophornis holotype, however, shows incredibly derivate features which are not found in any enantiornithe known.
First of all, this bird was a flightless giant: it was probably 1.5 tall and it weighed like an emu; the skull was incredibly bizarre, with two horn-like bone excretion in each jugal bone and incredibly large nasal holes that acted like a bony crest, which granted it the reputation of Nightmare cassowary*. The beak was partially hooked, suggesting a mostly carnivorous diet, but the overall gracile skull exclude the capacity of killing large animals.
Things became even more messed up with the discovery of the forelimbs of this bird: they were not just a wing, but an extremely long hand with two well-developed and partially fused phalanges (the first and second) with extremely elongated claws and an atrophied third one consisting of a single metacarpal. All these features make Criolophornis the platypus of birds, a true chimera of the ancient past.
Because of the two partially fused digits and long claws, the hands of Criolophornis were incapable of manipulating or grabbing objects but they were perfect for fast movements: it was speculated that these hands were used as a sickle, to repeatedly stab their prey or opponent. The unusual body of Criolophornis however makes this hypothesis unverifiable.
Several assumptions were made to understand the possible role of its large nasal crest and horn bones: at the moment there are two discretely accepted hypotheses:

• The sexual hypothesis: crests and horns in the animal world are often linked to sexual selection. The bony horns and a possibly colorful nasal crest could act as a perfect sexual display, which was used by males in order to attract the opposite sex. This hypothesis is the most accepted nowadays, but it still possesses some gaps: a colorful pattern could reduce the mimetic ability of Criolophornis, which would be extremely important for a predatory bird. The absence of other skeletons make also this suggestion unverifiable.

• The muscular-thermoregulation hypothesis: a scan of the nasal hole of Criolophornis has shown the presence of a very long and complex nasal passage, as complex as one of some ankylosaurids, which suggests a thermoregulation use, potentially useful for warming up the cold air of their cold oceanic environment. The bony horns of the jugal could have instead a muscular purpose, attaching powerful muscles that would help compensate for the gracile structure of the beak. 

Whatever the answer will be, Criolophornis will always be a surprising example of insular bizarreness and possibly one of the most interesting fossils from Mesozoic Antarctica. But the uniqueness of the paleobiota of Berkner Island is still far from being completely discovered...